1. Field of the Invention
This invention relates to a new process for preparing alkyl esters. More particularly, the invention relates to an improved process for preparing alkyl esters by the homologation of the corresponding next lower alkyl ester.
Specifically, the invention provides a new and improved process for preparing alkyl carboxylic acid esters, and preferably the ethyl esters of aliphatic carboxylic acids such as ethyl acetate, by the homologation of the corresponding next lower carbon number alkyl ester, such as the methyl ester, which process comprises contacting the lower carbon number alkyl ester with carbon monoxide and hydrogen in the presence of an iodide-or iodine-free catalyst composition comprising a ruthenium-containing compound, a cobalt-containing compound and a quaternary phosphonium salt or base and heating the resulting mixture to an elevated temperature and pressure for sufficient time to produce the desired higher carbon number alkyl ester, and removing the same from the reaction mixture.
2. Prior Art
Ethyl esters, such as ethyl acetate, are chemicals which have found wide use in industry. In addition to their use as solvents and diluents they may be pyrolyzed to form the valuable ethylene monomer.
Various methods have been used in the past for the production of the ethyl esters. The esters can be produced, for example, by reaction of the ethanol with the desired carboxylic acid, both components commonly being obtained from petroleum or agrichemical feedstocks. Synthesis of the ethyl esters from syngas would potentially be more economical and desirable.
It has been proposed, for example, to prepare methyl acetate from syngas and then convert the methyl acetate to the ethyl ester by further treatment with the syngas. British patent application No. 2,001,070A for instance, discloses a method for converting methyl acetate to ethyl acetate by use of a carbonylation catalyst containing cobalt and iodine. This method is limited, however, as it utilizes iodide-or iodine-containing promoters which are corrosive and difficult to utilize on a large commercial scale.
It is an object of the invention, therefore, to provide a new and improved process for preparing higher carbon number alkyl esters. It is a further object to provide a process for preparing alkyl esters from lower carbon number alkyl esters using a new and improved catalyst system. It is a further object to provide a new process for preparing ethyl esters from methyl esters of aliphatic carboxylic acids which gives good selectivity and yield of desired product. It is a further object to provide a process for preparing ethyl esters from methyl esters which avoids the use of iodine and iodide components and is adaptable for use on a large commercial scale. These and other objects will be apparent from the following detailed description thereof.